1. Field of the Invention
The present invention is generally related to a detection system for a propeller driven watercraft and, more particularly, to a system and method that detects the presence of human beings and other mammals above the surface of the water in the vicinity of a marine propulsion device behind the transom of a marine vessel.
2. Description of the Prior Art
Outboard motors have been used for many years to propel many different types of marine vessels. Sterndrive systems are also well known to those skilled in the art. Devices have been developed in an attempt to insulate human beings from potential harm caused by a rotating propeller of a marine vessel.
U.S. Pat. No. 5,074,488, which issued to Colling on Dec. 24, 1991, describes an aircraft engine deactivation apparatus. The apparatus is intended for stopping an aircraft engine while the aircraft is on the ground. The apparatus is for detection purposes and used to prevent a detected object from coming into contact with an engine driven propeller or a jet propulsion intake. A detector, preferably an infra-red radiation sensor, detects an object or person within a selected distance and within a selected area about the engine. Upon detection, a mechanical engine deactivator shuts down the engine. A by-pass switch renders the system inoperable, when desired.
U.S. Pat. No. 6,354,892, which issued to Staerzl on Mar. 12, 2002, discloses a detection device for a marine vessel. The detection device provides an infrared sensor with a tube having a central cavity in order to define a viewing angle which is more narrow than the inherent viewing angle of the infrared sensor. The central cavity of the tube also defines a line of sight and can be directed toward a particular region above the surface of the water near a marine vessel that is to be monitored for the presence of a heat generating object, such as a human being. An alarm circuit is responsive to signals from the infrared sensor and deactivates the marine propulsion system when a heat generating object is near the marine propulsion system. The length and diameter of the tube are selected to provide a desired viewing angle for the infrared sensor. An audible alarm output is provided if an attempt is made to manipulate a joystick that controls the marine propulsion system when a heat generating object is sensed by the infrared sensor.
U.S. Pat. No. 6,450,845, which issued to Snyder et al on Sep. 17, 2002, discloses a passive occupant sensing system for a watercraft. A tetherless occupant detector system uses an infrared sensor and a monitor circuit that provides a deactivation signal to an engine control unit and other control mechanisms in the event of an operator of the marine vessel leaving a preselected control position at its helm. The infrared sensor provides an output signal that is generally representative of the heat produced by an occupant within the controlled position of a marine vessel. The monitor circuit reacts to a sudden decrease in this heat magnitude and provides a deactivation signal in response to detecting this sudden decrease. The deactivation signal provided by the monitor circuit can be received by an engine control unit which then, in turn, deactivates a marine propulsion system. Alternatively, the deactivation signal itself can cause a deactivation of the marine propulsion system.
U.S. Pat. No. 5,418,359, which issued to Juds et al on May 23, 1995, describes a method and apparatus for detecting objects with range-dependent blocking. A method and apparatus is disclosed which allow the detection of an object by the generation of a radiated beam and a subsequent reflection by the object of a portion thereof. The detection of particulate object material due to a reflection of a portion of the generated beam is minimized.
U.S. Pat. No. 5,311,012, which issued to Juds et al on May 10, 1994, describes a method and apparatus for detecting objects with modifying gain and sensor means. This patent is generally similar to U.S. Pat. No. 5,418,359, described above.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
The use of infrared sensors to detect the presence of human beings or animals within a prescribed detection zone is well known to those skilled in the art. This type of system is commonly used to turn on lights when a human being passes through a detection zone. Any warm blooded animal can be sensed by an infrared detector.
An inherent problem associated with infrared detectors is that normal sunlight contains electromagnetic radiation that is within the infrared portion of the spectrum. As a result, an infrared detector can be erroneously triggered by reflected sunlight received by its sensing components. In the discussion below, a triggering of an infrared detection system by reflected sunlight, and not the heat generated by a human or other warm blooded animal, will be referred to as a “false” trigger because the infrared radiation is the result of reflected sunlight and not the result of the situation which is intended to be detected (the presence of a human or other warm blooded animal). When used in certain applications, such as in conjunction with a marine propulsion system, false triggering of an infrared sensor by reflected sunlight can have very deleterious effects. As an example, sunlight reflected off the surface of a body of water can be interpreted by an infrared sensing system as being indicative of the presence of a human being or marine mammal within the detection zone of the sensing system. This could falsely cause the triggering of a sensing circuit which could turn off an engine of the marine propulsion system. On a bright, sunny day, the detection circuit could be plagued with numerous false detections of this type.
It would therefore be significantly beneficial if a detection system could be employed to protect an area surrounding a propeller of a marine vessel in such a way that humans and marine mammals could be detected, but reflected sunlight would not produce false triggering of the infrared detection system.